The process of maskless lithography using photons, as disclosed in U.S. Pat. No. 5,691,541, issued Nov. 25, 1997 to Ceglio and Markle, utilizes a “programmable array of binary light switches” that generates a spatially modulated light field. The modulated light field is then relayed optically to the surface of a substrate that receives the desired circuit pattern. Ceglio and Markle discuss the use of extreme ultraviolet (EUV) light and a digital micro-mirror array in which the pixels comprise individual EUV mirrors that are tilted to either direct light to the substrate, or not. Ceglio and Markle disclose a programmable array comprising active elements that can be digitally programmed via direct electrical connection to a drive circuit. To program the pixels, it is usually proposed to have a matrix of wires that carry electrical signals to micro-mirrors at the intersections of pairs of wires. This arrangement becomes more difficult to fabricate as the circuit scale size is reduced, and limits the speed with which the whole array can be addressed.
Prior art optically addressed light modulators depend upon the relatively high refractive index changes that are available in the visible or ultraviolet spectral ranges, at wavelengths longer than the primary optical transitions relating to the first electronic excitation in optically transmissive media. The extreme ultraviolet, or soft X-ray region does not afford either high refractive indexes, or transmissive optical media, with which to construct the prior modulator designs. In the extreme ultraviolet region, practical modulators have to work in the reflective mode, or otherwise involve the use of sub-micron thickness films if they are to work in the transmission mode. An optically addressed modulator disclosed in U.S. Pat. No. 5,691,836, issued Nov. 25, 1997 to Clark, which operates by reflection from a mirror surface, involves an intermediate electronic drive circuit and the additional complexity of micro-lenses.
Accordingly, there is a need for novel modulators for extreme ultraviolet and soft X-ray radiation.